Geophysical data

Baltic Sea in winter

The Baltic Sea is a brackish inland sea, allegedly the largest body of brackish water in the world (other possibilities include the Black Sea and Hudson Bay). The Baltic Sea occupies a basin formed by glacial erosion during the last few Ice Ages.

Dimensions

The Baltic sea is about 1600 km (1000 mi) long, an average of 193 km (120 mi) wide, and an average of 55 m (180 ft, 30 fathoms) deep. The maximum depth is 459 m (1506 ft), on the Swedish side of the center. The surface area is about 377,000 km² (145,522 sq mi) and the volume is about 20,000 km³ (5040 cubic miles). The periphery amounts to about 8000 km (4968 mi) of coastline. [1]

Etymology

While Tacitus called it Mare Suebicum[2] after the Germanic people of the Suebi, the first to name it also as the Baltic Sea (Mare Balticum) was eleventh century German chronicler Adam of Bremen. The origin of the latter name is speculative. It might be connected to the Germanic word belt, a name used for two of the Danish straits, the Belts, while others claim it to be derived from Latinbalteus (belt).[3] However it should be noted that the name of the Belts might be connected to Danish bælte, which also means belt. Furthermore Adam of Bremen himself compared the Sea with a belt stating that the Sea is named so because it stretches through the land as a belt (Balticus, eo quod in modum baltei longo tractu per Scithicas regiones tendatur usque in Greciam). He might also have been influenced by name of legendary island mentioned in The Natural History by Pliny the Elder. Pliny mentions an island named Baltia (or Balcia) with reference to accounts of Pytheas and Xenophon. It is possible that Pliny refers to island named Basilia ("kingdom" or "royal") in On the Ocean by Pytheas. Baltia also might be derived from "belt" and means "near belt of sea (strait)". Meanwhile others have concluded that the name of the island originates from the Indo-European root *bhel meaning white, fair. Yet another explanation is that, while derived from the afore mentioned root, the name of the sea is related to naming for various forms of water and related substances in several European languages, that might have been originally associated colors found in swamps. Another explanation is that the name was related to swamp and originally meant "enclosed sea, bay" as opposed to open sea.[4]

In the Middle Ages the sea was known by variety of names, the name Baltic Sea started to dominate only after 16th century. Usage of Baltic and similar terms to denote the region east from the sea started only in 19th century.

Name in other languages

The Baltic Sea, in ancient sources known as Mare Suebicum (also known as Mare Germanicum),[5] is also known by the equivalents of "East Sea", "West Sea", or "Baltic Sea" in different languages:

In addition, Finnish, a Baltic-Finnic language, has calqued the Swedish term as Itämeri "East Sea", disregarding the geography (the sea is west of Finland), though understandably since Finns were under Swedish rule from Middle Ages until 1809.

In another Baltic-Finnic language, Estonian, it is called the West Sea (Läänemeri), with the correct geography (the sea is west of Estonia).

Sea ice

On the long-term average, the Baltic Sea is ice covered for about 45% of its surface area at the maximum annually. The ice-covered area during such a typical winter includes the Gulf of Bothnia, the Gulf of Finland, Gulf of Riga, Väinameri in the Estonian archipelago, the Stockholm archipelago and the Archipelago Sea. The remainder of the Baltic itself does not freeze during a normal winter, with the exception of sheltered bays and shallow lagoons such as the Curonian Lagoon. The ice reaches its maximum extent in February or March; typical ice thickness in the northernmost areas in the Bothnian Bay, the northern basin of the Gulf of Bothnia, is about 70 cm (28 in) for landfast sea ice. The thickness decreases farther south.

Freezing begins in the northern coast of Gulf of Bothnia typically in middle of November, reaching the open waters of Bothnian Bay in early January. The Bothnian Sea, the basin south of it, freezes on average in late February. The Gulf of Finland and the Gulf of Riga freeze typically in late January.

The ice extent depends on whether the winter is mild, moderate or severe. Severe winters can lead to ice formation around Denmark and southern Sweden. According to William Derham during the severe winters of 1703 and 1708 the ice cover permeated as far as the Danish straits, parts of the Bay of Bothnia and Gulf of Finland, in addition to coastal fringes in more southerly locations such as the Gulf of Riga. In recent years a typical winter produces only ice in the northern and eastern extremities of the Sea. In 2007 there was almost no ice formation except for a short period in March.[6]

In spring, the Gulf of Finland and of Bothnia normally thaw during late April, with some ice ridges persisting until May in the eastern Gulf of Finland. In the northernmost reaches of the Bothnian Bay ice usually stays until late May; by early June it is practically always gone.

During winter, fast ice, which is attached to the shoreline, develops first, rendering the ports unusable without the services of icebreakers. Level ice, ice sludge, pancake ice or rafter ice form in the more open regions. The gleaming expanse of ice is similar to the Arctic, with wind-driven pack ice and ridges up to 15 m, and was noted by the ancients. Offshore of the landfast ice the ice remains very dynamic all year, because of its thickness it is relatively easily moved around by winds and therefore makes up large ridges and piles up against the landfast ice and shores.

The ice cover is the main habitat only for a few larger species. The largest of them are the seals that both feed and breed on the ice, although the sea ice also harbors several species of algae that live in the bottom and inside brine pockets in the ice.

Hydrography

The Baltic Sea flows out through the Danish straits; however, the flow is complex. A surface layer of brackish water discharges 940 km³ per year into the North Sea. Due to the difference in salinity, a sub-surface layer of more saline water moving in the opposite direction brings in 475 km³ per year. It mixes very slowly with the upper waters, resulting in a salinity gradient from top to bottom, with most of the salt water remaining below 40 to 70 m deep. The general circulation is counter-clockwise: northwards along its eastern boundary, and south along the western one (Alhonen 88).

The difference between the outflow and the inflow comes entirely from fresh water. More than 250 streams drain a basin of about 1.6 million km², contributing a volume of 660 km³ per year to the Baltic. They include the major rivers of north Europe, such as the Oder, the Vistula, the Neman, the Daugava and the Neva. Additional fresh water comes from the difference of precipitation less evaporation, which is positive.

An important source of salty water are infrequent inflows of North Sea water into the Baltic. Such inflows, important to the Baltic ecosystem because of the oxygen they transport into the Baltic deeps, used to happen on average every four to five years until the 1980s. In recent decades they have become less frequent. The latest three occurred in 1983, 1993 and 2003 suggesting a new inter-inflow period of about ten years.

The water level is generally far more dependent on the regional wind situation than on tidal effects. However, tidal currents occur in narrow passages in the western parts of the Baltic Sea.

The significant wave height is generally much lower than that of the North Sea. Violent and sudden storms often sweep the surface, due to large transient temperature differences and a long reach of wind. Seasonal winds also cause small changes in sea level, of the order of 0.5 m (Alhonen 88).

Salinity

The Baltic Sea's salinity is much lower than that of ocean water (which averages 3.5%, or 35‰), as a result of abundant freshwater runoff from the surrounding land; indeed, runoff contributes roughly one-fortieth its total volume per year, as the volume of the basin is about 21,000 km³ and yearly runoff is about 500 km³. The open surface waters of the central basin have salinity of 6 to 8 ‰. At the semi-enclosed bays with major freshwater inflows, such as head of Finnish Gulf with Neva mouth and head of Bothnian gulf with close mouths of Lule, Tornio and Kemi, the salinity is considerably lower. Below 40 to 70 m, the salinity is between 10 and 15 ‰ in the open Baltic Sea, and more than this near Danish Straits.

The flow of fresh water into the sea from approximately two-hundred rivers and the introduction of salt from the South builds up a gradient of salinity in the Baltic Sea. Near the Danish straits the salinity is close to that of the Kattegat, but still not fully oceanic, because the saltiest water that passes the straits is still already mixed with considerable amounts of outflow water. The salinity steadily decreases towards North and East. At the northern part of the Gulf of Bothnia the water is no longer salty and many fresh water species live in the sea. The salinity gradient is paralleled by a temperature gradient. These two factors limit many species of animals and plants to a relatively narrow region of Baltic Sea.

The most saline water is vertically stratified in the water column to the north, creating a barrier to the exchange of oxygen and nutrients, and fostering completely separate maritime environments.[7]

Regional emergence

Much of modern Finland is former seabed or archipelago: illustrated are sea levels immediately after the last ice age.

The land is still emerging isostatically from its subsident state, which was caused by the weight of the last glaciation. The phenomenon is known as post-glacial rebound. Consequently, the surface area and the depth of the sea are diminishing. The uplift is about eight millimetres per year on the Finnish coast of the northernmost Gulf of Bothnia. In the area, the former seabed is only gently sloped, leading to large areas of land being reclaimed in, geologically speaking, relatively short periods (decades and centuries).

The Northern Baltic Sea lies between the Stockholm area, southwestern Finland and Estonia. The Western and Eastern Gotland Basins form the major parts of the Central Baltic Sea or Baltic proper. The Bornholm Basin is the area east of Bornholm, and the shallower Arkona Basin extends from Bornholm to the Danish isles of Falster and Zealand.

Land use

The Baltic sea drainage basin is roughly four times the surface area of the sea itself. About 48% of the region is forested, with Sweden and Finland containing the majority of the forest, especially around the Gulfs of Bothnia and Finland.

About 20% of the land is used for agriculture and pasture, mainly in Poland and around the edge of the Baltic Proper, in Germany, Denmark and Sweden. About 17% of the basin is unused open land with another 8% of wetlands. Most of the latter are in the Gulfs of Bothnia and Finland.

The rest of the land is heavily populated.

Demographics

About 85 million people live in the Baltic drainage basin, 15 million within 10 km (6 mi) of the coast and 29 million within 50 km (31 mi) of the coast. Around 22 million live in population centers of over 250,000. 90% of these are concentrated in the 10 km (6 mi) band around the coast. Of the nations containing all or part of the basin, Poland includes 45% of the 85 million, Russia 12%, Sweden 10% and the others (see below) less than 6% each.

From that time the waters underwent a geologic history summarized under the names listed below. Many of the stages are named after marine animals (e.g. the Littorinamollusk) that are clear markers of changing water temperatures and salinity.

The factors that determined the sea's characteristics were the submergence or emergence of the region due to the weight of ice and subsequent isostatic readjustment, and the connecting channels it found to the North Sea-Atlantic, either through the straits of Denmark or at what are now the large lakes of Sweden, and the White Sea-Arctic Sea.

History

At the time of the Roman Empire, the Baltic Sea was known as the Mare Suebicum or Mare Sarmaticum. Tacitus in his AD 98 Agricola and Germania described the Mare Suebicum, named for the Suebi tribe, during the spring months, as a brackishsea when the ice on the Baltic Sea broke apart and chunks floated about. The Suebi eventually migrated south west to reside for a while in the Rhineland area of modern Germany, where their name survives in the historic region known as Swabia. The Sarmatian tribes inhabited Eastern Europe and southern Russia. Jordanes called it the Germanic Sea in his work the Getica.

Since the Viking age, the Scandinavians have called it "the Eastern Lake" (Austmarr, "Eastern Sea", appears in the Heimskringla and Eystra salt appears in Sörla þáttr), but Saxo Grammaticus recorded in Gesta Danorum an older name Gandvik, "-vik" being Old Norse for "bay", which implies that the Vikings correctly regarded it as an inlet of the sea. (Another form of the name, "Grandvik", attested in at least one English translation of Gesta Danorum, is likely to be a misspelling.)

In addition to fish the sea also provides amber, especially from its southern shores. The bordering countries have traditionally provided lumber, wood tar, flax, hemp, and furs. Sweden had from early medieval times also a flourishing mining industry, especially on iron ore and silver. Poland had and still has extensive salt mines. All this has provided for rich trading since the Roman times.

In the early Middle Ages, Vikings of Scandinavia built their trade empire all around the Baltic. Later, there were fights for control over the sea with Wendish tribes dwelling on the southern shore. The Vikings also used the rivers of Russia for trade routes, finding their way eventually to the Black Sea and southern Russia. This Viking-dominated period is also referred to as Viking Age.

In the 12th century, there was intensification of Slavic piracy. Starting in the 11th century, the southern and eastern shores of the Baltic were settled by Germans (and to a lesser extent by Dutch, Danes and Scots) in the course of the Ostsiedlung. The Polabian Slavs were gradually assimilated by the Germans.[9]Denmark gradually gained control over most of the Baltic coast, until she lost much of her possessions after being defeated in the 1227 Battle of Bornhöved.

In the 13th to 17th centuries, the strongest economic force in Northern Europe became the Hanseatic league, which used the Baltic Sea to establish trade routes between its member cities. In the sixteenth and early seventeenth centuries, Polish-Lithuanian Commonwealth, Denmark and Sweden fought wars for Dominium Maris Baltici ("Ruling over the Baltic Sea"). Eventually, it was the Swedish Empire that virtually encompassed the Baltic Sea. In Sweden the sea was then referred to as Mare Nostrum Balticum ("Our Baltic Sea").

In the eighteenth century, Russia and Prussia became the leading powers over the sea. The Great Northern War, ending with Sweden's defeat, brought Russia to the eastern coast. Since then, Russia was a dominating power in the Baltic. Russia's Peter the Great saw the strategic importance of the Baltic and decided to found his new capital, Saint Petersburg at the mouth of the Neva river at the east end of the Gulf of Finland. There was much trading not just within the Baltic region but also with the North Sea region, especially eastern England and the Netherlands: their fleets needed the Baltic timber, tar, flax and hemp.

During the Second World War, Germany reclaimed all of the southern shore and much of the eastern by occupying Poland and the Baltic states. In 1945, the Baltic Sea became a mass grave for retreating soldiers and refugees on torpedoed troop transports. The sinking of the MV Wilhelm Gustloff remains the worst maritime disaster, killing (very roughly) 9,000 people. In 2005, a Russian group of scientists found over five thousand airplane wrecks, sunken warships, and other material mainly from the Second World War, lying at the bottom of the sea.

Since the end of World War II, various nations, including the Soviet Union, the United Kingdom, the United States, and Germany, have disposed of chemical weapons in the Baltic Sea, raising concerns of environmental contamination.[10] Even now fisherman accidentally retrieve some of these materials: the most recent available report from the Helsinki Commission notes that four small scale catches of CW munitions representing approximately 105 kilograms (231 lbs) of material were reported in 2005. This is a reduction from the 25 incidents representing 1,110 kilograms (2,447 lbs) of material in 2003.[11]

Winter storms begin arriving in the region during October. These have caused numerous shipwrecks, such as the sinking of the ferry M/S Estonia en route from Tallinn, Estonia, to Stockholm, Sweden, in 1994, which claimed the lives of hundreds. Older, wood-based shipwrecks such as the Vasa tend to remain well-preserved, as the Baltic's cold and brackish water does not suit the shipworm.

Biology

Approximately 100,000 km2 (38,610 sq mi) of the Baltic's seafloor (a quarter of its total area) is a variable dead zone. The more saline (and therefore denser) water remains on the bottom, isolating it from surface waters and the atmosphere. This leads to decreased oxygen concentrations within the zone. It is mainly bacteria that grow in it, digesting organic material and releasing hydrogen sulfide. Because of this large anaerobic zone, the seafloor ecology differs from that of the neighbouring Atlantic.

The low salinity of the Baltic sea has led to the evolution of many slightly divergent species, such as the Baltic Sea herring, which is a smaller variant of the Atlantic herring. The benthic fauna consists mainly of Monoporeia affinis, which is originally a freshwater species. The lack of tides has affected the marine species as compared with the Atlantic.

Economy

Construction of the Great Belt Bridge in Denmark (completed 1997) and the Oresund Bridge-Tunnel (completed 1999), linking Denmark with Sweden, provided a highway and railroad connection between Sweden and the Danish mainland (the Jutland Peninsula). The undersea tunnel of the Oresund Bridge-Tunnel provides for navigation of large ships into and out of the Baltic Sea. The Baltic Sea is the main trade route for export of Russian petroleum. Many of the countries neighboring the Baltic Sea have been concerned about this, since a major oil leak in a seagoing tanker would be disastrous for the Baltic—given the slow exchange of water. The tourism industry surrounding the Baltic Sea is naturally concerned about oil pollution.

Resort towns

The Helsinki Convention

1974 Convention

For the first time ever, all the sources of pollution around an entire sea were made subject to a single convention, signed in 1974 by the then seven Baltic coastal states. The 1974 Convention entered into force on 3 May 1980.

1992 Convention

In the light of political changes and developments in international environmental and maritime law, a new convention was signed in 1992 by all the states bordering on the Baltic Sea, and the European Community. After ratification the Convention entered into force on 17 January 2000. The Convention covers the whole of the Baltic Sea area, including inland waters and the water of the sea itself, as well as the seabed. Measures are also taken in the whole catchment area of the Baltic Sea to reduce land-based pollution. The Convention on the Protection of the Marine Environment of the Baltic Sea Area, 1992, entered into force on 17 January 2000.

The governing body of the Convention is the Helsinki Commission,[12] also known as HELCOM, or Baltic Marine Environment Protection Commission. The present contracting parties are Denmark, Estonia, the European Community, Finland, Germany, Latvia, Lithuania, Poland, Russia and Sweden.

The ratification instruments were deposited by the European Community, Germany, Latvia and Sweden in 1994, by Estonia and Finland in 1995, by Denmark in 1996, by Lithuania in 1997 and by Poland and Russia in November 1999.

References

^Tacitus, Germania (book): Ergo iam dextro Suebici maris litore Aestiorum gentes adluuntur, quibus ritus habitusque Sueborum, lingua Britannicae propior.[1] - Upon the right of the Suevian Sea the AEstyan nations reside, who use the same customs and attire with the Suevians; their language more resembles that of Britain.[2]